#1 Naraku (InuYasha)
He has always been my favorite bad guy. No weird monologues, no odd sentimentality, he's not insane and screams random things. He don't care about anything really and his plots are surprisingly clever (the only smart character in InuYasha) IMO, he's the best villain.

#2 Bakura (Yugioh)
Total badass blood-thirsty psychopath out for a vengeance several millennia. He sure can hold a grudge. Need I say more?

#3 Ulquiorra (Bleach)
Cold melancholic killer who thinks almost everyone is trash. Not to mention his epic release states.

#4 Mukuro Rokudo (Katekyo Hitman Reborn)
Was a bad guy, turned good guy (just like all of Tsuna's opponents).

#5 Hisoka (Hunter x Hunter) or Akabane (GetBackers)
A total weirdo, but absolutely deadly. Does what he wants and will do anything for a great battle.